Materials that include retroreflective structures such as microcubes or glass beads typically possess a property such that incident light is reflected back in a direction from which the light originates. This makes the materials popular for use in a wide range of products that require a retroreflective attribute. The materials are particularly useful for safety applications, including signage, construction barriers, traffic barriers, personal protection gear and the like.
Several methods are known to make materials retroreflective. One method uses microscopic beads to form what is generally referred to as “beaded sheets.” The microscopic beads may include a metallized coating to improve performance, i.e., optical reflectance. The microscopic beads may be deposited on a surface of sheeting or film, or be partially or fully embedded in the sheeting. A second method uses microprisms, commonly referred to as “prismatic sheeting.” Prismatic sheeting uses microstructures such as cube-cornered, triangles, hexagons, squares and/or rectangles incorporated or otherwise formed on sheeting or film to return back reflected light.
During manufacturing of prismatic films, a potential exists for trapping volatile gases between a polymer film and a metallic tooling belt which is typically used to form a pattern in the film. The volatile gases are typically emitted during the softening and melting of the polymer films. If these gases are trapped between the tooling and the polymer film, they may lead to visual defects such as bubbles or voids and affect the quality of the resulting prismatic film.
Accordingly, a need exists for a strategy of reducing the potential for, and ideally eliminating or substantially so, trapped volatile gases along the prismatic film during its formation.